It [LVM] does this by, in effect, standing between the filesystem and the physical disks, mediating all their interactions.

This sounds like the typical solution by introducing an extra level of indirection. I have no problem with that as it makes life easier in a number of ways.

However, that made me think about performance since disk I/O is one of the key resources (hence the multiple cache levels, SSD, etc).

Has the performance impact of LVM (compared to traditional partitioning schemes) been measured? Can anything be done to tune its performance? For example, what is the impact of changing the size of the extents from the default 32MB? Is there any point in trying to match this size to the size of the (hardware) disk cache. Conversely, should we buy disks that have a certain amount of cache?